The present invention relates to a method and apparatus for a printing system. More specifically, the invention relates to the manufacture of printer rolls and belts for printing systems. The features of the present invention are useful in the printing arts and more particularly in electrophotographic printing.
In the well-known process of electrophotographic printing, a charge retentive surface, typically known as a photoreceptor, is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder known as xe2x80x9ctoner.xe2x80x9d Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto by fusing the toner image to the paper to form a permanent record of the image to be reproduced.
Several components in the electrophotographic printing process described above are in the form of polymeric rolls and belts. Fusing rolls, which are used to fix the toner image on a substrate, represent a component that is typically in the form of polymeric rolls or belts. Also included among these components are bias charge rolls (BCRS) and bias transfer rolls (BTRS) which electrostatically charge the photoreceptor. In addition such rolls and belts include the pressure or backup roll used with a fusing roll to fix the toner image on a substrate, donor rolls which transfer oil to the fuser roll that assists in releasing the toner from the fuser roll, intermediate transfer rolls and belts that transfer developed images, photoconductive belts and rolls, and those belts and rolls used in Hybrid Scavangeless Development (HSD). All of these a polymeric rolls and belts are typically manufactured by spraying or by dipping of the above mentioned components.
It is particularly difficult to manufacture fuser rolls and belts because of the elevated temperatures and pressures to which these rolls are subjected and the accurate size and finish requirements necessary to insure proper copy quality.
The fusing of the toner image to the paper to form a permanent record of the image is an important part of the xerographic process. Fusing of the toner image is typically done by heat fixation. The heat fixation may be in the form of radiation, conduction, convection or induction. Most modern xerographic processes utilize conduction heating of the toner image to adhere the image to the paper. To accomplish this purpose a fusing roll is placed in rolling contact with a backup roll forming a nip. The paper having the transferred toner image is fed between the rolls through the nip. Heat from the fusing roll together with the pressure within the nip, between the fuser roll and the backup roll, serve to fuse the image to the paper. Heat is typically applied internally within the roll and is transferred through the substrate of the roll onto the periphery of the roll and onto the paper.
The rolls typically include a thermally conductive substrate with a surface layer which is also thermally conductive. To assure uniform transfer of the image onto the paper, typically the fuser roll coating is conformable to the paper. For example, the coating may be in the form of a rubber or polymer material, e.g. a fluoroelastomer coating. Applying fluorelastomer and other rubber type coatings to fuser roll substrates are fraught with many problems. The coating may be applied to the substrate by two typical methods which are dipping of the substrate into a bath of coating solution or spraying the surface of the substrate with the coating material.
Spraying is the typical method for the manufacture of fluoroelastomer rollers and it is slow and costly. Also, the spraying process requires having the coating solution in a form that is volatile including many volatile organic chemicals. Further, the spraying process is prone to air pockets or pits forming in the coating. These pits or air pockets in the coating material of the roll result in improper fusing and poor image quality. Because of the nature of the spray process, much of the coating material is lost in the atmosphere requiring an excess amount of the expensive coating material utilized. Also, the loss of the volatile chemicals result in expensive containment costs for systems to contain the volatile chemicals as well as disposal costs of these materials.
This invention is intended to alleviate at least some of the above-mentioned problems for at least some of the several components in the electrophotographic printing process described above which are in the form of polymeric rolls and belts.
A more recent process attempts to apply coating solution by dripping material over a horizontally rotating cylinder. With this process a portion of the material adheres to the cylinder and the remainder drips from the cylinder. The amount of material added to the roll is not precisely controlled as the percentage that adheres varies as parameters change over the production run. Also the material forms a wavy coating surface where the material is poured. This so called flow coating method may be enhanced by means of a flexible wiper applied to the surface of the roll as the coating is applied, as described in U.S. Pat. No. 5,871,832 the disclosure ot which is incorporated herein by reference. This tends to provide a more even coating thickness.
During the processing in accordance with the prior art there is little attention paid to the end surfaces of the rolls. It is generally desirable to coat the ends of the roll to close the edges of the coating and seal the metal end plates. It is a purpose of this invention to provide an apparatus and method for coating the ends of a fuser roll in conjunction with the coating of the cylindrical surface of such rolls.
A flow coating process is adapted to apply a coating to the end surfaces of a cylindrical fuser roll. To accomplish this purpose a coating station is designed for insertion within the coating operation of a fuser production line. The coating station comprises a nozzle mounted in the path of the production line for applying a flouroelastomer (polymeric) coating solution to a cylindrical fuser roll. The fuser roll is secured on a transport for movement through the coating station in a direction transverse to the axis of the roll. The fuser roll is mounted on the transport for rotary movement about its longitudinal axis. The process control stops the fuser roll in the station and rotates the roll under the nozzle while the nozzle translates over the roll in a motion which is parallel to the axis of the roll. To coat the ends of the roll, the nozzle is held stationery at the ends of the roll, while the roll is rotated.
A pair of arms are mounted on a transfer head in the station for movement parallel to and coordinated with the nozzle. Each of the arms are constructed to independently rotate towards and away from the fuser roll between a retracted position and an operational position. Rotation of the arms is controlled so that only one nozzle is operational at a given time. In the operational position, the arm assembly is located at the end of the fuser roll and one of the arms extends generally horizontal under the nozzle.
When the nozzle begins its application cycle, it will generally be positioned above one end of the fuser roll. According to this invention, the arm assembly is positioned at the same axial location as the nozzle either just ahead or just behind the roll. In the operative position the stream of solution from the nozzle will flow vertically downward immediately adjacent to the end of the roll. The operative arm is rotated under the stream to cause a deflection of the stream towards the end of the roll.
Each of the arms are formed having a near edge and a far edge relative to the end of the fuser roll. The near edge is constructed having a surface which is shaped to deflect the coating stream towards the end surface of the roller. The far edge is shaped to direct excess coating solution away from the roller to avoid splattering the cylindrical surface and marring the finish coating of the cylinder.